Even after carefully executed informed consent procedures are carried out, patients may not fully process the nature and implications of the medical research in which they are participating. This study focuses on the cognitive functioning of patients in hospital-based clinical research. Participation in medical research is a stressful circumstance that provides a natural experiment in which patients' level of understanding and reasoning about personally stressful content (their illness and treatment regimens) is examined in relation to their cognitive functioning with regard to nonstress-related content and their level of anxiety. Participants include child, adolescent, and adult in-patients and normal volunteers at the NIH Clinical Center. Psychological assessments include standardized tests and interviews.